Recently, as information and communication technology is rapidly developed, a ubiquitous society based on information and communication technology has been realized.
In order to be connected to information and communication equipment anywhere and at any time, sensors in which computer chips having a communication function are mounted should be installed in social facilities. Therefore, power supply to these facilities and sensors is a new problem. Further, as the variety of kinds of portable devices including not only mobile phones but also Bluetooth headsets, music players, such as iPods, etc., is rapidly increased, battery charging burdens a worker with time and additional work. In order to solve such a problem, wireless power transmission technology is receiving attention.
Wireless power transmission or wireless energy transfer is technology for wirelessly transmitting electrical energy from a transmitter to a receiver using electromagnetic induction. Electric motors or transformers using electromagnetic induction began to be used in the 1800s and, since then, electrical energy transmission methods using radiation of electromagnetic waves, such as radio waves, lasers, high-frequency waves and microwaves, have been attempted. Electric toothbrushes and some wireless razors, which are frequently used, are charged using electromagnetic induction.
Wireless energy transfer that is available at present may be classified into a magnetic induction method, an electromagnetic resonance method, an RF transmission method using a short-wavelength wireless frequency, etc.
The magnetic induction method is technology using a phenomenon in which, when current is applied to one of two coils disposed adjacent to each other, a magnetic flux occurs and then creates electromotive force in the other coil, and has now been rapidly commercialized in small devices such as mobile phones. The magnetic induction method may transmit power of hundreds of kW at most and have high efficiency, but the maximum transmission distance is 1 cm or less and thus the coils must be disposed adjacent to a charger or the floor.
The electromagnetic resonance method uses electric fields or magnetic fields instead of electromagnetic waves or current. The electromagnetic resonance method is scarcely influenced by electromagnetic wave problems and is thus safe for other electronic devices or humans. On the other hand, the electromagnetic resonance method is disadvantageous in that it is applicable only at a limited distance and in a limited space and in that the energy transmission efficiency is rather low.
The short-wavelength wireless power transmission method, i.e., the RF transmission method, uses the fact that energy of a radio wave type may be directly transmitted or received. Such technology is an RP-type wireless power transmission method using a rectenna, and the rectenna, which is a portmanteau word of “antenna” and “rectifier”, means an element for converting RF power directly into DC power. That is, the RF method is technology in which AC radio waves are converted into DC, and, recently, as the efficiency of the RF method is improved, research on commercialization of the RF method is vigorously carried out.
The wireless power transmission technology is applicable to various industries, i.e., not only to the mobile industry but also to vehicle, IT, railway and household appliance industries.
In general, a wireless power transmitter is provided with coils for wireless power transmission, hereinafter referred to as “transmission coils”, and various shields for preventing electromagnetic fields, generated by the transmission coils, or AC power from being transmitted to a control substrate are used.
As representative shields, there are a magnetic shielding sheet and a sendust block formed by processing magnetic metal powder.
However, most conventional sendust blocks provided in wireless power transmitters have poor insulating properties and thus require separate insulating sheets to be attached thereto, and various electronic parts and terminals may not be integrated with the sendust blocks owing to the poor insulating properties thereof.
Particularly, a wireless power transmitter mounted in a vehicle requires strong robustness to vibration of the vehicle during driving and thus the necessity to integrate various electronic parts and terminals with the sendust block is increased.
Further, with regard to the characteristics of wireless charging, the sendust block requires not only high insulating performance of an AC component but also requires high magnetic permeability in order to maximize wireless power transmission efficiency.